Facile and selective polynitrations at the 4-pyrazolyl dual backbone: straightforward access to a series of high-density energetic materials

Nitro-functionalized energetic materials are still needed to meet new safety, performance and chemical accessibility demands. The problem of multiple C-nitrations on N-containing heterocycles was resolved successfully for the 4,4-bipyrazole scaffold. A progression of gradually functionalized 3-nitro-4,4'-bipyrazole (2), 3,3'-dinitro-4,4'-bipyrazole (3), 3,5'-dinitro-4,4'-bipyrazole (4), 3,3',5-trinitro-4,4'-bipyrazole (5) and 3,3',5,5'-tetranitro-4,4'-bipyrazole (6) was obtained in excellent yields by highly selective direct nitrations of 4,4-bipyrazole (1). All synthesized polynitro derivatives 3-6 exhibit high decomposition temperatures of above 290 degrees C. The introduction of three (5) and four nitro groups (6) into the 4,4'-bipyrazole scaffold yields insensitive and thermally stable high explosives with excellent densities and detonation properties. The anhydrous structures of compounds 2-6 were obtained by low-temperature XRD. In addition, the performance of compounds 5 and 6 was investigated with a small scale shock reactivity test.